Field
The present disclosure relates generally to the field of semiconductor device manufacturing and, more particularly, to low temperature formation of silicon nitride thin films.
Description of the Related Art
Spacers are widely used in semiconductor manufacturing as structures to protect against subsequent processing steps. For example, nitride spacers formed beside gate electrodes can be used as a mask to protect underlying source/drain areas during doping or implanting steps.
As the physical geometry of semiconductor devices shrinks, the gate electrode spacer becomes smaller and smaller. The spacer width is limited by the nitride thickness that can be deposited conformably over the dense gate electrodes lines. Thus, the nitride spacer etching process is preferred to have a high ratio of spacer width to nitride layer thickness as deposited.
Current PEALD silicon nitride processes in general suffer from anisotropic etch behavior when used to deposit on a three-dimensional structure, such as a trench structure. In other words, the film deposited on the sidewalls of a trench or fin or another three dimensional feature display inferior film properties as compared to film on the top region of the feature. The film quality may be sufficient for the target application on the top of the trench, or on planar regions of a structured wafer, but not on the sidewalls or other non-horizontal or vertical surfaces.
FIGS. 1A and 1B illustrate a typical example of a silicon nitride film, which could be used, for example, in spacer applications. The film was deposited at 400° C. using a conventional PEALD process, not a process described in the present application. FIG. 1A illustrates the film after it was deposited on a three-dimensional surface but prior to being etched by HF. An etching process was then performed by dipping the workpiece in 0.5% BF for about 60 seconds. FIG. 1B illustrates the extent to which vertical portions of the silicon nitride film etch to a greater extent than the horizontal portions of the film. The film thicknesses are indicated in nanometers. Structures such as these would not generally survive further processing, such as in a FinFET spacer application.